A method for preparing a denitrification denitrogenation and dephosphorization agent by carbon reduction of waste gypsum and an application method thereof

Abstract

The application discloses a method for preparing a denitrification denitrogenation and dephosphorization agent by carbon reduction of waste gypsum and an application method thereof, and belongs to the technical field of wastewater treatment. The method comprises the following steps: carrying out a high-temperature reduction reaction on waste gypsum and coke to obtain a calcium sulfide product; dissolving the calcium sulfide with water and filtering to remove insoluble substances; and mixing the liquid with a waste incineration fly ash washing liquid to obtain the denitrification denitrogenation and dephosphorization agent. The denitrification denitrogenation and dephosphorization agent is added into water in a denitrification denitrogenation reactor by using a metering pump, the calcium sulfide serves as an electron donor for sulfur autotrophic denitrification and a pH neutralizer, and the calcium ions serve as a precipitant for dephosphorization, so that denitrogenation of wastewater or simultaneous denitrogenation and dephosphorization is realized.

Description

Technical Field

[0001] This invention relates to the fields of solid waste resource utilization and simultaneous deep denitrification and phosphorus removal in wastewater treatment plants. More specifically, it relates to simultaneous denitrification and phosphorus removal agents prepared from waste gypsum and fly ash from waste incineration plants, and their application techniques and methods. Background Technology

[0002] Nitrification-heterotrophic denitrification has always been the mainstream technology for wastewater nitrogen removal. Through an aerobic biological process, organic nitrogen and ammonia nitrogen in the water are converted into nitrate nitrogen. The wastewater is then returned to an anoxic tank, where organic matter in the wastewater serves as an electron donor, and heterotrophic denitrifying microorganisms convert nitrate nitrogen into nitrogen gas. Heterotrophic denitrification technology faces several obstacles in meeting increasingly stringent total nitrogen standards for wastewater discharge: First, a high reflux ratio is required to achieve higher discharge standards, leading to excessively large water treatment tank footprints, high energy consumption, and significantly increased costs. Second, due to the long retention time of wastewater in septic tanks and drainage pipes, microbial degradation of organic matter consumes some carbon sources, resulting in insufficient carbon sources and a low carbon-to-nitrogen ratio in the wastewater entering the wastewater treatment plant, failing to meet the organic carbon requirements of heterotrophic denitrification. Third, in cases of insufficient carbon sources, especially for high-nitrogen industrial wastewater, anaerobic biological filters are commonly added after the secondary sedimentation tank, relying on heterotrophic denitrifying bacteria to remove nitrogen by adding organic carbon. However, the addition of agents such as sodium acetate leads to excessively high denitrification costs, and improper dosage control results in excessively high COD in the effluent, causing secondary pollution.

[0003] To compensate for the shortcomings of heterotrophic denitrification and meet the needs of advanced denitrification in water treatment, sulfur autotrophic denitrification technology has rapidly developed in recent years as a representative autotrophic denitrification technology. Sulfur autotrophic denitrification involves facultative anaerobic microorganisms such as denitrifying thiobacilli using inorganic carbon as a carbon source to complete anabolism, while simultaneously using sulfur and reducing sulfur compounds (thiosulfates, sulfites, sulfides, iron sulfide minerals, and sulfur) as electron donors to reduce nitrates to nitrogen. Iron sulfide minerals, such as pyrite and pyrrhotite, have attracted significant attention due to their low cost and abundant production. However, a major problem with iron sulfide mineral autotrophic denitrification is its extremely slow reaction rate and excessive land occupation, which cannot meet the needs of wastewater treatment plant denitrification projects. Sulfur, as an electron donor, has a faster denitrification reaction rate than iron sulfide minerals and is becoming the mainstream direction for sulfur autotrophic denitrification development.

[0004] Sulfur autotrophic denitrification technology has advantages such as abundant and inexpensive sulfur resources, low sludge production, and low treatment costs, making it a hot topic in current nitrogen removal research and engineering. However, the autotrophic denitrification process using sulfur as an electron donor can lead to water acidification. Limestone and other carbonates are typically used as pH-stabilizing media. Existing sulfur-limestone autotrophic denitrification systems use a mixture of limestone and elemental sulfur particles in a specific ratio as packing material, or a mixture of limestone powder and sulfur granulated and used as packing material, loaded into a reaction filter column for wastewater treatment. The limestone continuously dissolves during the treatment process, thus buffering the pH decrease.

[0005] Currently, autotrophic nitrogen removal technology for sulfur still faces the following prominent problems:

[0006] (1) The problem of slow denitrification speed of solid sulfur autotrophic denitrification materials. Sulfur autotrophic denitrification materials, including sulfur and iron sulfide minerals, can significantly reduce denitrification costs compared with sodium acetate, but the slow denitrification speed is a major problem. Because sulfur autotrophic denitrification materials are all insoluble solids, their interaction with microorganisms requires complex electron transfer media during microbial metabolism. This is the key factor restricting the denitrification reaction speed and the fundamental reason for the slow speed of sulfur autotrophic denitrification. Usually, heterotrophic denitrification anaerobic biological deep filter with sodium acetate can stably meet the control requirements of nitrate nitrogen and total nitrogen when the hydraulic retention time is 25-40 minutes. However, the existing sulfur autotrophic denitrification technology requires a hydraulic retention time of more than 100 minutes, and the hydraulic retention time of natural iron sulfide autotrophic denitrification is mostly required to be more than 4 hours. This leads to excessively high investment in the construction of sulfur autotrophic denitrification treatment ponds and poor economic efficiency. How to improve the biological reaction rate of autotrophic denitrification and make the hydraulic residence time of the denitrification reaction reach or approach the hydraulic residence time of heterotrophic denitrification is a key technical problem that urgently needs to be solved.

[0007] (2) Simultaneous nitrogen and phosphorus removal. With the increasing pilot-scale implementation of water environmental protection and the continuous improvement of drainage standards, many regions require domestic sewage treatment plants to meet the Class IV standard for surface water (dissolved oxygen 3 mg / L, COD 30 mg / L, total phosphorus 0.3 mg / L, total nitrogen 1.5 mg / L). Sewage treatment plants not only face the problem of nitrogen removal but also the problem of phosphorus removal. Existing sewage treatment plants generally use chemical precipitation-magnetic flocculation separation of iron and aluminum salts for phosphorus removal and heterotrophic denitrification deep bed filters for nitrogen removal. Although iron sulfide minerals can simultaneously remove nitrogen and phosphorus, the nitrogen removal rate is too slow and cannot meet the requirements of sewage treatment plants for nitrogen removal rate. Sulfur autotrophy has a faster nitrogen removal rate than sulfides such as pyrite and pyrrhotite, but nitrogen removal methods using sulfur as an electron donor have not achieved significant phosphorus removal effects. How to achieve rapid nitrogen removal and simultaneous phosphorus removal in the same sulfur autotrophic denitrification filter is a difficult problem in the field of water treatment. Summary of the Invention

[0008] Based on extensive static and dynamic synchronous denitrification and phosphorus removal experiments, this invention provides a method for preparing denitrification and phosphorus removal agents by carbon reduction of waste gypsum. This method is then applied to the deep synchronous denitrification and phosphorus removal of wastewater to solve the problems existing in the prior art and to provide technical support for deep sulfur autotrophic denitrification and phosphorus removal in wastewater.

[0009] To achieve its objectives, the present invention employs the following technical solution:

[0010] This invention first provides a method for preparing denitrification, denitrification, and phosphorus removal agents by carbon reduction of waste gypsum, including the following methods:

[0011] Method 1:

[0012] (1) Mix waste gypsum and coke at a mass ratio of 4~8:1, reduce calcium sulfate to calcium sulfide at a high temperature of not less than 1150℃, and cool under a protective atmosphere to obtain solid calcium sulfide product.

[0013] (2) Dissolve the solid calcium sulfide product in water and filter to remove insoluble matter to obtain calcium sulfide solution; the filtered residue (mainly composed of coke and calcium silicate compounds) is washed with water and used as coke feedstock for calcium sulfide production or disposed of as general waste, and the washing water is used to dissolve calcium sulfide.

[0014] (3) Wash the fly ash from the waste incineration with water at a water-ash mass ratio of 3~5:1 to dissolve the calcium chloride and calcium hydroxide in the fly ash (the main components of which are calcium chloride, calcium hydroxide, calcium carbonate, calcium sulfate, and silicate) to obtain fly ash washing liquid; the fly ash washing residue (the main components of which are calcium carbonate, calcium sulfate, and silicate, and the dioxins and heavy metals in the fly ash are also retained in the residue) is used to replace part of the waste gypsum ingredients in the production of calcium sulfide;

[0015] (4) The calcium sulfide solution is combined with the fly ash washing liquid to obtain an alkaline mixture with a calcium ion to sulfur ion mass ratio of 2~10:1. The main components of the solution are calcium sulfide, calcium chloride and calcium hydroxide, which are used as sulfur autotrophic denitrification denitrification and phosphorus removal agents.

[0016] Method 2:

[0017] Waste gypsum and coke are mixed at a mass ratio of 4 to 8:1, and calcium sulfate is reduced to calcium sulfide at a high temperature of not less than 1150℃. The mixture is then cooled under a protective atmosphere to obtain solid calcium sulfide product.

[0018] Add 1-10% by mass of sodium aluminate to the solid calcium sulfide product and mix thoroughly to obtain a denitrification denitrification and phosphorus removal agent.

[0019] Method 3:

[0020] Waste gypsum and coke are mixed at a mass ratio of 4 to 8:1, and calcium sulfate is reduced to calcium sulfide at a high temperature of not less than 1150℃. The mixture is then cooled under a protective atmosphere to obtain solid calcium sulfide product.

[0021] The solid calcium sulfide product and industrial by-product sulfur are mixed at a molar ratio of calcium sulfide to sulfur of 1:3~4, and the mixture is homogeneous to obtain the denitrification denitrification and phosphorus removal agent.

[0022] Method 4:

[0023] Waste gypsum and coke are mixed at a mass ratio of 4 to 8:1, and calcium sulfate is reduced to calcium sulfide at a high temperature of not less than 1150℃. The mixture is then cooled under a protective atmosphere to obtain solid calcium sulfide product.

[0024] The solid calcium sulfide product and industrial by-product sulfur are mixed at a molar ratio of 1:3 to 4. Then, 1-5% sodium aluminate is added according to the total mass of the solid calcium sulfide product and industrial by-product sulfur. The mixture is then thoroughly mixed to obtain the denitrification denitrification and phosphorus removal agent.

[0025] Method 5:

[0026] (1) Mix waste gypsum and coke at a mass ratio of 4~8:1, reduce calcium sulfate to calcium sulfide at a high temperature of not less than 1150℃, and cool under a protective atmosphere to obtain solid calcium sulfide product.

[0027] (2) Dissolve the solid calcium sulfide product in water and filter to remove insoluble matter to obtain a calcium sulfide solution;

[0028] (3) Wash the fly ash from the waste incineration with water at a water-ash mass ratio of 3:1 to 5:1 to obtain fly ash washing liquid; use water to wash and dissolve the calcium chloride and calcium hydroxide in the fly ash (the main components are calcium chloride, calcium hydroxide, calcium carbonate, calcium sulfate and silicate) to obtain fly ash washing liquid; use the fly ash washing residue (the main components are calcium carbonate, calcium sulfate and silicate, and dioxins and heavy metals in the fly ash are also retained in the residue) as raw material for calcium sulfide production.

[0029] (4) Combine the calcium sulfide solution with the fly ash washing liquid to obtain an alkaline mixture with a calcium ion to sulfur ion mass ratio of 2 to 10:1; add industrial by-product sulfur to the alkaline mixture according to the molar ratio of calcium sulfide to sulfur of 1:3 to 1:4, and mix evenly to obtain the denitrification denitrification and phosphorus removal agent.

[0030] The choice of the five methods depends on the availability and price of raw materials such as sulfur, sodium aluminate, and fly ash, as well as the quality of the wastewater. Method 1's denitrification and phosphorus removal agent solution mainly consists of calcium sulfide, calcium chloride, and calcium hydroxide. It relies on calcium sulfide as an electron donor for nitrogen removal and on calcium ions and a high pH value for phosphorus precipitation. This method is suitable for applications with long hydraulic retention times and low phosphorus removal requirements. Method 2's denitrification and phosphorus removal agent involves adding sodium aluminate to the solid calcium sulfide product. Phosphorus removal mainly relies on the precipitation of aluminum phosphate compounds, making it suitable for applications with high phosphorus removal requirements. Methods 3 and 5's denitrification and phosphorus removal agents are formulated by mixing solid calcium sulfide product or a mixture of calcium sulfide solution and fly ash washing liquid with industrial byproduct sulfur. This utilizes the ability of sulfides to react with sulfur to generate dissolved polysulfide species, making it suitable for applications where sulfur is inexpensive and readily available. Method 4 uses a denitrification denitrification and phosphorus removal agent that combines solid calcium sulfide products with industrial byproducts such as sulfur and sodium aluminate. This method has both low denitrification costs and excellent phosphorus removal effects.

[0031] This invention further provides a method for applying the above-mentioned denitrification nitrogen and phosphorus removal agent, which is carried out according to the following steps:

[0032] (1) Add enriched cultured Thiobacillus denitrification liquid to the denitrification reactor, wherein the reactor includes, but is not limited to, a filter, a completely mixed reaction tank, a fluidized bed, and a membrane bioreactor;

[0033] (2) Fill the reactor with the wastewater to be treated, and add nitrate and the denitrification nitrogen and phosphorus removal agent to the influent to maintain the nitrate nitrogen concentration in the influent of the denitrification nitrogen removal reactor at 10-100 mg / L and the sulfur ion concentration at 10-150 mg / L. Return the effluent to the influent for circulation and incubation for 3-10 days to allow sufficient sulfur autotrophic microorganisms to grow in the reactor and achieve a nitrogen removal efficiency of more than 60%.

[0034] (3) After the microorganisms in the denitrification reactor mature, the reactor is operated with influent and effluent according to the designed flow rate. The denitrification and phosphorus removal agent is diluted with water to prepare a solution with a mass concentration of 0.1-10%, and added to the influent of the denitrification reactor using a metering pump. The addition ratio is 1:1~1.5 based on the mass ratio of nitrate nitrogen to reduced sulfur in the wastewater to be treated. Reduced sulfur serves as an electron donor for autotrophic denitrification microorganisms, calcium ions and hydroxide ions serve as phosphorus removal agents to promote the growth of apatite, and aluminum ions serve as phosphate precipitants, thereby achieving simultaneous denitrification and phosphorus removal of wastewater.

[0035] Furthermore, the concentrations of nitrate nitrogen, total nitrogen, phosphate, total phosphorus, calcium ions, and pH value in the effluent are monitored. The dosage of the denitrification and phosphorus removal agent is adjusted to meet the denitrification requirements, so that the total nitrogen, total phosphorus, and pH value of the effluent from the denitrification reactor are stable and meet the standards, and the concentrations of dissolved calcium ions and chloride ions are kept as low as possible.

[0036] The mechanism and beneficial effects of this invention are reflected in:

[0037] (1) Using waste gypsum and coke as raw materials, calcium sulfate is reduced to calcium sulfide at a high temperature of not less than 1150℃ (Equation 1), and the calcium sulfide product is obtained by cooling under a protective atmosphere, thus realizing the high-value and resource utilization of waste gypsum. The waste gypsum and coke mixture or pre-formed granules are preheated, dried and dehydrated by the flue gas discharged from the reduction furnace (Equation 2), reducing the energy consumption of the reduction process.

[0038] (1)

[0039] (2)

[0040] (2) The solid calcium sulfide product is dissolved in water and filtered to remove insoluble matter. Preferably, the calcium sulfide is dissolved in wastewater at a sewage treatment plant. The filtered residue is mainly residual carbon, which is washed clean with wastewater and returned to the feedstock for calcium sulfide production. The washing liquid is used to dissolve calcium sulfide, which reduces waste residue and wastewater discharge, improves coke utilization, and reduces water and energy consumption.

[0041] (3) The main components of waste incineration fly ash are calcium chloride, calcium hydroxide, calcium carbonate, and calcium sulfate. It contains dissolved salts and toxic and harmful organic matter, and is a hazardous solid waste that is difficult to treat and utilize. The main components of water-washed fly ash are calcium chloride and calcium hydroxide. The washing liquid is used to prepare denitrification and phosphorus removal agents. It not only plays a role in neutralizing sulfur oxidation and producing acid during the microbial sulfur autotrophic denitrification process, but also plays a role in removing phosphorus and reducing the cost of wastewater denitrification and phosphorus removal agents. It also solves the problem of disposing of calcium chloride dissolved salts in waste incineration fly ash. Heavy metals, dioxins, and other toxic and harmful organic matter in waste incineration fly ash are enriched in the residue. The main components are calcium carbonate and calcium sulfate. It is used as a raw material for the production of calcium sulfide. The high-temperature reducing atmosphere completely destroys dioxins and other toxic and harmful organic matter, and transforms heavy metals into insoluble sulfides, which is conducive to the resource recovery of heavy metals in fly ash.

[0042] (4) The calcium sulfide solution and the fly ash washing liquid are combined to obtain an alkaline mixture with calcium sulfide, calcium chloride and calcium hydroxide as the main components. This results in a low-cost autotrophic denitrification and dephosphorization agent, which meets the requirements of electron donors, hydroxyl ions and calcium ions for simultaneous denitrification and dephosphorization of wastewater. This low-cost method realizes the resource utilization of waste fly ash washing liquid, which is helpful for the treatment, disposal and resource utilization of waste incineration fly ash.

[0043] (5) Dissolved reduced sulfur is an electron donor for autotrophic denitrification. In aqueous solution, reduced sulfur is more easily migrated than sulfur and can directly cross the cell membrane of denitrifying thiobacilli to carry out denitrification reaction in the cell (Equation 3). This overcomes the electron transfer barrier between solid sulfur and denitrifying microorganisms, greatly improves the rate of sulfur autotrophic denitrification, and provides a brand-new technical solution for solving the problem of sulfur autotrophic denitrification rate.

[0044] Autotrophic denitrification reaction:

[0045] (3)

[0046] (6) The simultaneous denitrification and phosphorus removal agent formulated in this invention utilizes the alkalinity of lime to stabilize the pH of the water in the wastewater denitrification and phosphorus removal reactor at 8-9. Under the condition of meeting the wastewater discharge pH requirements (pH 6-9), it promotes the growth of hydroxyapatite and phosphorus removal. The growth rate of apatite crystals is affected by their supersaturation. The higher the solution pH and calcium ion concentration, the higher the supersaturation, the faster the apatite grows, and the lower the residual phosphate concentration in the water. Under the premise of not affecting the microbial metabolic rate and not exceeding the discharge standards, increasing the pH as much as possible is beneficial to the removal of phosphate. Adding calcium chloride during the preparation of lime-sulfur solution increases the calcium ion concentration in lime-sulfur, promoting phosphorus removal. This couples the requirements of sulfur autotrophic denitrification and phosphorus removal in the simultaneous denitrification and phosphorus removal process for the concentration of reduced sulfur species, pH, and calcium ion concentration.

[0047] Phosphorus removal reaction:

[0048] (4)

[0049] Hydroxyapatite solubility product:

[0050] (5)

[0051] (7) Eliminating the hazards of toxic and harmful organic substances such as dioxins in fly ash. During the fly ash washing process, dioxins and heavy metals, which are difficult to dissolve in water, mainly remain in the washing residue. The washing residue is used as an ingredient in the production of calcium sulfide, where dioxins are completely decomposed and heavy metals are fixed by sulfide under a high temperature above 1150℃ and a reducing atmosphere. Even if there are trace amounts of organic matter in the fly ash washing liquid, when it enters the alkaline solution composed of calcium sulfide, calcium chloride, and calcium hydroxide as a denitrification and phosphorus removal agent, it comes into contact with oxygen in the air during preparation, storage, and use. The reduction of sulfur ions, the reaction with oxygen to produce a small amount of highly active free radicals, and the action of microorganisms during anaerobic denitrification can all decompose and transform the trace amounts of toxic and harmful organic substances in the fly ash washing liquid of waste incineration.

[0052] (8) The carbothermic reduction of calcium sulfate to prepare calcium sulfide is a classic technical method. The calcium sulfide produced is used in depilatory agents for animal skins, insecticides, and in the production of luminescent paints and thiourea. It is also used as a precipitant for heavy metal ions in wastewater. This invention has found that the sulfide ions in calcium sulfide have excellent denitrification efficiency for autotrophic microorganisms. The calcium ions and the hydroxyl groups in the calcium sulfide are conducive to the synergistic precipitation of phosphorus in the water, thus achieving efficient and simultaneous denitrification and phosphorus removal. Detailed Implementation

[0053] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0054] Example 1

[0055] (1) Waste gypsum and coke are mixed at a mass ratio of 6:1 in a tubular electric furnace at a high temperature of 1150-1200℃ to reduce calcium sulfate to calcium sulfide. The product is obtained by cooling under a protective atmosphere.

[0056] (2) Dissolve calcium sulfide in the effluent from the secondary sedimentation tank of the sewage treatment plant. The ratio of water to calcium sulfide is 10:1. Stir the calcium sulfide in a container to dissolve it, and filter to remove insoluble matter.

[0057] (3) Wash the filter residue with water from the secondary sedimentation tank. The volume ratio of water to filter residue is 2:1. The filter residue is drained and treated as general waste. The washing water is used to dissolve calcium sulfide.

[0058] (4) Using water to wash and dissolve calcium chloride and calcium hydroxide in the fly ash from waste incineration at a water-ash mass ratio of 4:1, fly ash washing liquid and fly ash washing residue are used as ingredients for the preparation of calcium sulfide.

[0059] (5) Combine the aforementioned calcium sulfide solution with fly ash washing liquid to obtain an alkaline mixture with a calcium ion to sulfur ion mass ratio of 3:1, which is used as a sulfur autotrophic denitrification and dephosphorization agent.

[0060] (6) Use a metering pump to add the denitrification nitrogen and phosphorus removal agent to the influent of the denitrification filter at a mass ratio of 1:1 of nitrate nitrogen to sulfur ions in the secondary sedimentation tank.

[0061] (7) Add enriched culture of denitrifying sulfur bacteria to the denitrification filter. After 5 days of incubation and culture, the sulfur autotrophic microorganisms will be basically mature and attached to the surface of the packing. Sulfide ions serve as electron donors for the autotrophic denitrifying microorganisms, while calcium ions and hydroxide ions serve as phosphorus removal agents to promote the growth of apatite, thereby achieving simultaneous denitrification and phosphorus removal of wastewater.

[0062] (8) Monitor the concentrations of nitrate nitrogen, total nitrogen, phosphate, total phosphorus, calcium ions and pH value in the effluent. First, fix the amount of denitrification and phosphorus removal agent to meet the denitrification requirements. Then, adjust the ratio of calcium sulfide solution to fly ash washing liquid in the denitrification and phosphorus removal agent according to the phosphorus removal requirements. Finally, ensure that the total nitrogen in the effluent of the denitrification reactor is <5mg / L, the total phosphorus is <0.2mg / L and the pH value is 7-9, all of which stably meet the standard of quasi-IV surface water quality, and keep the concentrations of residual calcium ions and chloride ions in the wastewater as low as possible.

[0063] Example 2

[0064] (1) Waste gypsum and coke are reduced to calcium sulfide in a tubular electric furnace at a mass ratio of 6:1 at a high temperature of 1150-1200℃. The calcium sulfide product is obtained by cooling under a protective atmosphere.

[0065] (2) Mix the calcium sulfide product with industrial sulfur powder at a molar ratio of 1:4 for calcium sulfide to sulfur, and then add sodium aluminate at a mass ratio of 3% of the mixture to obtain a denitrification denitrification and phosphorus removal agent.

[0066] (3) Use the effluent from the secondary sedimentation tank to dissolve the denitrification and phosphorus removal agent to prepare a solution with a mass concentration of 5%.

[0067] (4) Use a metering pump to add the denitrification and phosphorus removal agent to the influent of the denitrification filter according to the mass ratio of reduced sulfur to nitrate nitrogen in the secondary sedimentation tank water of 1.3:1.

[0068] (5) Add enriched culture of denitrifying sulfur bacteria to the denitrification filter. After 5 days of incubation and culture, the sulfur autotrophic microorganisms will be basically mature and attached to the surface of the packing. Dissolved reduced sulfur serves as the electron donor for the autotrophic denitrifying microorganisms, and aluminum ions serve as the phosphorus removal precipitant, thus achieving simultaneous denitrification and phosphorus removal of wastewater.

[0069] (6) Monitor the concentrations of nitrate nitrogen, total nitrogen, phosphate, total phosphorus, calcium ions and pH value in the effluent. First, fix the amount of denitrification and phosphorus removal agent to meet the denitrification requirements. Then, adjust the proportion of sodium aluminate in the denitrification and phosphorus removal agent according to the phosphorus removal requirements. Finally, make the total nitrogen in the effluent of the denitrification reactor <5mg / L, the total phosphorus <0.2mg / L and the pH value 6-8, and make all water quality indicators stably meet the standard of quasi-IV surface water quality.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a denitrification and phosphorus removal agent by carbon reduction of waste gypsum, characterized in that, Follow these steps: (1) Mix waste gypsum and coke at a mass ratio of 4~8:1, reduce calcium sulfate to calcium sulfide at a high temperature of not less than 1150℃, and cool under a protective atmosphere to obtain solid calcium sulfide product. (2) Dissolve the solid calcium sulfide product in water and filter to remove insoluble matter to obtain calcium sulfide solution; the filtered residue is washed with water and used as coke feedstock for calcium sulfide production or disposed of as general waste, and the washing water is used to dissolve calcium sulfide. (3) Wash the fly ash containing calcium chloride and calcium hydroxide with water at a water-ash mass ratio of 3~5:1 to obtain fly ash washing liquid; the fly ash washing residue is used to replace part of the waste gypsum material in the production of calcium sulfide. (4) The calcium sulfide solution is combined with the fly ash washing liquid to obtain an alkaline mixture with a calcium ion to sulfur ion mass ratio of 2~10:

1. The main components of the solution are calcium sulfide, calcium chloride and calcium hydroxide, which are used as denitrification denitrification and phosphorus removal agents.

2. A method for preparing a denitrification and phosphorus removal agent by carbon reduction of waste gypsum, characterized in that, Follow these steps: (1) Mix waste gypsum and coke at a mass ratio of 4~8:1, reduce calcium sulfate to calcium sulfide at a high temperature of not less than 1150℃, and cool under a protective atmosphere to obtain solid calcium sulfide product. (2) Dissolve the solid calcium sulfide product in water and filter to remove insoluble matter to obtain a calcium sulfide solution; (3) Wash the fly ash containing calcium chloride and calcium hydroxide with water at a water-ash mass ratio of 3:1 to 5:1 to obtain fly ash washing liquid; the fly ash washing residue is used to replace part of the waste gypsum material in the production of calcium sulfide. (4) Combine the calcium sulfide solution with the fly ash washing liquid to obtain an alkaline mixture with a calcium ion to sulfur ion mass ratio of 2 to 10:1; add industrial by-product sulfur to the alkaline mixture according to the molar ratio of calcium sulfide to sulfur of 1:3 to 1:4, and mix evenly to obtain the denitrification denitrification and phosphorus removal agent.

3. A denitrifying denitrifying and phosphorus-removing agent prepared by the method of preparing denitrifying denitrifying and phosphorus-removing agent by carbon reduction of waste gypsum according to any one of claims 1 to 2.

4. A method for applying the denitrification nitrogen removal and phosphorus removal agent according to claim 3, characterized in that, Follow these steps: (1) Add enriched culture of Thiobacillus denitrification to the denitrification reactor; (2) Fill the reactor with the wastewater to be treated, and add nitrate and the denitrification nitrogen and phosphorus removal agent to the influent to maintain the nitrate nitrogen concentration in the influent of the denitrification nitrogen removal reactor at 10-100 mg / L and the sulfur ion concentration at 10-150 mg / L. Return the effluent to the influent for circulation and incubation for 3-10 days to allow sufficient sulfur autotrophic microorganisms to grow in the reactor and achieve a nitrogen removal efficiency of more than 60%. (3) After the microorganisms in the denitrification reactor mature, the reactor is operated with influent and effluent according to the designed flow rate. The denitrification and phosphorus removal agent is diluted with water to prepare a solution with a mass concentration of 0.1-10%, and added to the influent of the denitrification reactor using a metering pump. The addition ratio is 1:1~1.5 based on the mass ratio of nitrate nitrogen to reduced sulfur in the wastewater to be treated. Reduced sulfur serves as an electron donor for autotrophic denitrification microorganisms, calcium ions and hydroxide ions serve as phosphorus removal agents to promote the growth of apatite, and aluminum ions serve as phosphate precipitants, thereby achieving simultaneous denitrification and phosphorus removal of wastewater.

5. The application method of the denitrification nitrogen removal and phosphorus removal agent according to claim 4, characterized in that: Monitor the concentrations of nitrate nitrogen, total nitrogen, phosphate, total phosphorus, calcium ions, and pH value in the effluent. Adjust the dosage of denitrification and phosphorus removal agent to meet the denitrification requirements, so that the total nitrogen, total phosphorus, and pH value of the effluent from the denitrification reactor are stable and meet the standards, and the concentrations of dissolved calcium ions and chloride ions are as low as possible.